The widespread removal of lead antiknock additive from gasoline and the rising fuel-quality demands of high-performance internal-combustion engines have compelled petroleum refiners to install new and modified processes for increased “octane,” or knock resistance, in the gasoline pool. Refiners have relied on a variety of options to upgrade the gasoline pool, including higher-severity catalytic reforming, higher FCC (fluid catalytic cracking) gasoline octane, isomerization of light naphtha and the use of oxygenated compounds. Such key options as increased reforming severity and higher FCC gasoline octane result in a higher aromatics content of the gasoline pool at the expense of low-octane heavy paraffins.
Refiners are also faced with supplying reformulated gasoline to meet tightened automotive emission standards. Reformulated gasoline differs from the traditional product in having a lower vapor pressure, lower final boiling point, increased content of oxygenates, and lower content of olefins, benzene and aromatics. Benzene content generally is being restricted to 1% or lower, and is limited to 0.8% in U.S. reformulated gasoline. Gasoline aromatics content is likely to be lowered, particularly as distillation end points (usually characterized as the 90% distillation temperature) are lowered, since the high-boiling portion of the gasoline which thereby would be eliminated usually is an aromatics concentrate. Since aromatics have been the principal source of increased gasoline octanes during the recent lead-reduction program, severe restriction of the benzene/aromatics content and high-boiling portion will present refiners with processing problems. These problems have been addressed through such technology as isomerization of light naphtha to increase its octane number, isomerization of butanes as alkylation feedstock, and generation of additional light olefins as feedstock for alkylation and production of oxygenates using FCC and dehydrogenation. This issue often has been addressed by raising the cut point between light and heavy naphtha, increasing the relative quantity of naphtha to an isomerization unit. The performance of light-naphtha isomerization catalysts thus is increasingly important in refinery economics.
U.S. Pat. No. 2,939,896 B1 teaches isomerization of paraffinic hydrocarbons using a catalyst containing platinum, halogen and a sulfate of aluminum, magnesium and/or zirconium deposited on activated alumina. The patent does not disclose additional metal components of the catalyst, however. U.S. Pat. No. 5,036,035 B1 teaches a catalyst, and its use in isomerization, containing sulfated zirconium oxide or hydroxide and a platinum-group metal. The patent teaches that reduction of the platinum-group metal is not favorable.
U.S. Pat. No. 4,918,041 B1, U.S. Pat. No. 4,956,519 B1 and European Patent Application 0 666 109 A1 disclose a sulfated catalyst, and its use in isomerization, comprising an oxide or hydroxide of Group III or Group IV; oxide or hydroxide of Groups V, VI or VII; and oxide or hydroxide of Group VIII; '109 also discloses a component from a list of Group VIII metals and metal combinations.
U.S. Pat. No. 3,915,845 B1 discloses a catalyst and its use comprising a platinum-group metal, Group IVA metal, halogen and lanthanide in an atomic ratio to platinum-group metal of 0.1 to 1.25. U.S. Pat. No. 5,493,067 B1 teaches that isoparaffins and olefins are alkylated by contact with a solid superacid such as sulfated zirconia optionally containing added metals and containing added heteropolyacids or polyoxoanions.
U.S. Pat. No. 5,310,868 B1 and U.S. Pat. No. 5,214,017 B1 teach catalyst compositions containing sulfated and calcined mixtures of (1) a support containing an oxide or hydroxide of a Group IV-A element, (2) an oxide or hydroxide of a Group VI, VII, or VIII metal, (3) an oxide or hydroxide of a Group I-B, II-B, III-A, III-B, IV-A, V-A metal, and (4) a metal of the lanthanide series.
U.S. Pat. No. 5,212,136 B1 discloses a solid super acid catalyst useful in alkylation processes comprising sulfated and calcined mixtures of a support of an oxide or hydroxide of a Group IV-A element, an oxide or hydroxide of molybdenum, and an oxide or hydroxide of a Group I-B, II-B, III-A, III-B, IV-B, V-A or VI-A metal other than molybdenum or a metal of the lanthanide series.